Tyran Marguerite, Tallet Agnes, Resbeut Michel, Ferre Marjorie, Favrel Veronique, Fau Pierre, Moureau-Zabotto Laurence, Darreon Julien, Gonzague Laurence, Benkemouche Ahcene, Varela-Cagetti Leonel, Salem Naji, Farnault Bertrand, Acquaviva Marie-Aimee, Mailleux Hugues
Department of Radiation-Oncology, Institut Paoli-Calmettes, Marseille, France.
J Appl Clin Med Phys. 2018 Sep;19(5):463-472. doi: 10.1002/acm2.12398. Epub 2018 Jun 30.
This study evaluates the benefit of a virtual bolus method for volumetric modulated arc therapy (VMAT) plan optimization to compensate breast modifications that may occur during breast treatment.
Ten files were replanned with VMAT giving 50 Gy to the breast and 47 Gy to the nodes within 25 fractions. The planning process used a virtual bolus for the first optimization, then the monitors units were reoptimized without bolus, after fixing the segments shapes. Structures and treatment planning were exported on a second scanner (CT) performed during treatment as a consequence to modifications in patient's anatomy. The comparative end-point was clinical target volume's coverage. The first analysis compared the VMAT plans made using the virtual bolus method (VB-VMAT) to the plans without using it (NoVB-VMAT) on the first simulation CT. Then, the same analysis was performed on the second CT. Finally, the level of degradation of target volume coverage between the two CT using VB-VMAT was compared to results using a standard technique of forward-planned multisegment technique (Tan-IMRT).
Using a virtual bolus for VMAT does not degrade dosimetric results on the first CT. No significant result in favor of the NoVB-VMAT plans was noted. The VB-VMAT method led to significant better dose distribution on a second CT with modified anatomies compared to NoVB-VMAT. The clinical target volume's coverage by 95% (V95%) of the prescribed dose was 98.9% [96.1-99.6] on the second CT for VB-VMAT compared to 92.6% [85.2-97.7] for NoVB-VMAT (P = 0.0002). The degradation of the target volume coverage for VB-VMAT is not worse than for Tan-IMRT: the median differential of V95% between the two CT was 0.9% for VMAT and 0.7% for Tan-IMRT (P = 1).
This study confirms the safety and benefit of using a virtual bolus during the VMAT planning process to compensate potential breast shape modifications.
本研究评估虚拟容积法在容积调强弧形放疗（VMAT）计划优化中对补偿乳房治疗期间可能发生的乳房形态改变的益处。
对10份病例重新进行VMAT计划，给予乳房50 Gy、淋巴结47 Gy，分25次照射。计划过程中，首次优化时使用虚拟容积，然后在固定射野形状后，在不使用容积的情况下重新优化监测单位。由于患者解剖结构的改变，在治疗期间进行的第二次扫描（CT）上导出结构和治疗计划。比较终点为临床靶区的覆盖情况。首次分析将在首次模拟CT上使用虚拟容积法制定的VMAT计划（VB-VMAT）与未使用该方法的计划（NoVB-VMAT）进行比较。然后，在第二次CT上进行相同的分析。最后，将使用VB-VMAT的两次CT之间靶区覆盖的降级水平与使用正向计划多野技术（Tan-IMRT）的标准技术的结果进行比较。
在首次CT上，VMAT使用虚拟容积不会降低剂量学结果。未发现支持NoVB-VMAT计划的显著结果。与NoVB-VMAT相比，VB-VMAT方法在解剖结构改变的第二次CT上导致明显更好的剂量分布。在第二次CT上，VB-VMAT的规定剂量的95%（V95%）临床靶区覆盖率为98.9% [96.1-99.6]，而NoVB-VMAT为92.6% [85.2-97.7]（P = 0.0002）。VB-VMAT靶区覆盖的降级不比Tan-IMRT更差：两次CT之间V95%的中位差异对于VMAT为0.9%，对于Tan-IMRT为0.7%（P = 1）。
本研究证实了在VMAT计划过程中使用虚拟容积以补偿潜在乳房形态改变的安全性和益处。
